Cross Relaxation Research Articles

Preparation of Dy3+/Tm3+ Co-doped Phosphate Glasses by Melt Method and its Luminescence Properties

In this paper, P2O5 matrix materials were used to prepare Dy3+/Tm3+ phosphate glasses with different concentrations by high temperature melt method. The emission spectrum of Dy3+/Tm3+co-doped glass samples were measured under 350nm excitation. High-efficiency green and blue down-conversion emissions were already observed. Based on the intensity of the emission peaks of samples doped with different concentrations of Dy3+/Tm3+, It can be assumed that an energy transfer process is occurring between Dy3+/Tm3+, i.e. the energy transfer process between the two kinds of ions is Dy3+ to Tm3+ and Tm3+to Dy3+, respectively. Finally, the energy transfer between Dy3+/Tm3+ was further illustrated by testing the fluorescence decay lifetime of the samples. It was found that the increased probability of cross relaxation of ions in glasses doped with 0.8mol% Dy3+/0.2mol% Tm3+ caused the fluorescence quenching of Dy3+ ions, and a fluorescence color shift from blue to white was observed in the range of 0.2-0.7mol% Dy3+. CIE coordinates of the 0.2mol% Tm3+/0.7mol% Dy3+ co-doped phosphate glasses sample are (0.33, 0.32), which is extremely approximate to the standards of equivalent energy white light for illumination (0.33,0.33). The results indicate that Dy3+/Tm3+ has a significant contribution in the down-conversion mechanism.

Influence of Bi+ ions on photoluminescence properties of Tm2O3 doped borotellurite glasses for the near-infrared emission applications

This paper reports the influence of bismuth ions (Bi+) on photoluminescence properties of Tm2O3 doped borotellurite based glasses (BTGS) with the composition (64-y)B2O3–30TeO2 – 5NaF- yBi2O3–1Tm2O3, where y = 0, 4, 8, 12 and 16 wt% for the near-infrared (NIR) emission applications. All glasses were prepared using the melt-quenching method and confirmed to exhibit amorphous nature by the X-ray diffraction (XRD) technique. The absorption spectra in the wavelength range of 300–2100 nm and emission spectra in the wavelength range of 400–2200 nm were studied. Increase of y wt. % value increases the 3H4→3F4 and 3F4→3H6 (near-infrared, NIR emission) intensities due to cross-relaxation (CR) and enhanced energy transfer processes between the active centres (Bi+ and Tm3+ ions), which are strongly influenced by bismuth content (Bi+) in the glass matrix. Based on Judd-Ofelt theory, the intensity parameters Ω2, Ω4 and Ω6 for each glass were determined and found to follow the trend Ω2>Ω4>Ω6 similar to the recently reported photonic glasses. Using the Ωλ parameters and reduced matrix elements, the calculation for the emission transition probability (A), radiative lifetime (τR), branching ratio (βR) and emission-cross sections (σPE) of 3H4, 3H5, and 3F4 energy levels were done and found to be slightly higher than fluoride and other oxide-based glasses because of the high density and refractive index values of the present samples.

Concentration and temperature dependence behaviors of photoluminescence and scintillation properties of Lu2O3:Pr single crystals

Praseodymium doped lutecia (Lu1−xPrx)2O3 (x = 0.003, 0.006 and 0.01) single crystals have been prepared by optical floating zone (OFZ) method. The concentration and temperature dependence of photoluminescence and scintillation properties, including photoluminescence excitation (PLE) and photoluminescence (PL), PL decay, X-ray excited luminescence (XEL) and afterglow curves were systematically investigated. Both onward (Pr(S6)→Pr(C2)) and inverse (Pr(C2)→Pr(S6)) energy transfers are observed in Lu2O3:Pr. It is found that with the increasing of Pr3+ concentration, the Pr(S6)→Pr(C2) energy transfers efficiency increases. And the PL decay time becomes faster due to the increasing cross relaxation transition. Meanwhile, as the temperature increases (78–500 K), the onward and inverse energy transfer efficiencies between the two kinds of Pr3+ are enhanced simultaneously. The highest scintillation efficiency is Lu2O3:0.6%Pr and afterglow levels of obtained single crystals were comparable.

Upconversion nanoparticles@AgBiS2 core-shell nanoparticles with cancer-cell-specific cytotoxicity for combined photothermal and photodynamic therapy of cancers.

UCNPs@AgBiS2 core-shell nanoparticles that AgBiS2 coated on the surface of upconversion nanoparticles (UCNPs) was successfully prepared through an ion exchange reaction. The photothermal conversion efficiency of AgBiS2 can be improved from 14.7% to 45% due to the cross relaxation between Nd ions and AgBiS2. The doping concentration of Nd ions played a critical role in the production of reactive oxygen species (ROS) and enhanced the photothermal conversion efficiency. The NaYF4:Yb/Er/Nd@NaYF4:Nd nanoparticles endows strong upconversion emissions when the doped concentration of Nd ions is 1% in the inner core, which excites the AgBiS2 shell to produce ROS for photodynamic therapy (PDT) of cancer cells. As a result, the as-prepared NaYF4:Yb/Er/Nd@NaYF4:Nd@AgBiS2 core-shell nanoparticles showed combined photothermal/photodynamic therapy (PTT/PDT) against malignant tumors. This work provides an alternative near-infrared light-active multimodal nanostructures for applications such as fighting against cancers.

Development of bright orange-reddish color emitting material from Sm3+-doped Y2O3 based borosilicate glasses for solid state lighting materials

The glass having B2O3-Na2O-Y2O3-SiO2:Sm2O3 were fabricated to study its various Spectroscopic and radiative properties. For NBS-glass samples the trend for JO-parameters Ω4 > Ω2 > Ω6 except NBS-01 glass sample. The experimental (βexp) branching ratio are compared with theoretical (βcal) branching ratio and are in agreement with each other. The obtained values of the color-coordinates for NBS-Sm samples are located within orange-reddish region. The CCT-value for all NBS-Sm glasses are 1720 K. IH study suggest the dipole type of interaction between Sm3+-ions. The possible reason for this non-exponential behavior is non radiative energy transfer through resonance energy transfer between Sm3+−ions and cross relaxation between different energy levels of Sm3+-ions in NBS-glass matrix. The Study suggest the potential of NBS-Sm glass in advance display devices application emitting orange-reddish color.

Synthesis and luminescent properties of rare earths doped Gd<sub>2</sub>Te<sub>4</sub>O<sub>11</sub> tellurite phosphors

A series of rare earth Dy<sup>3+</sup>, Tb<sup>3+</sup>, Eu<sup>3+</sup> singly doped Gd<sub>2</sub>Te<sub>4</sub>O<sub>11</sub> (GTO) tellurite phosphors with intrinsic polarity are prepared by hydrothermal method. The phase structures, morphologies and thermal stabilities of these phosphors are characterized. Their luminescence properties are tested in detail. The results show that all those phosphors are crystalized into single phase of digadolinium tellurite with short rod-like shape. The maximum size in the axial direction is microns. The phosphor has good thermal stability. For the GTO:Dy<sup>3+</sup>, the fluorescence emission under UV excitation is mainly located in the yellow-green region. The optimal doping concentration corresponding to the strongest excitation and emission is 2.5%, and the CIE color coordinates are (0.39, 0.43). The fluorescence decay curve shows that the lifetime of the GTO:Dy<sup>3+</sup> on <sup>4</sup>F<sub>9/2</sub> energy level decreases gradually with doping concentration of Dy<sup>3+</sup> increasing, which may be related to the cross relaxation (CR) between Dy<sup>3+</sup> ions. For the GTO:Eu<sup>3+</sup>, the fluorescence emission under UV excitation is mainly located in the red region and orange-red region. The emission intensity is enhanced with the doping concentration of Eu<sup>3+</sup> increasing. When the doping concentration is 10%, the CIE color coordinates are (0.62, 0.38), which are located in the orange-red region with high color purity. The fluorescence lifetime of Eu<sup>3+</sup> on <sup>5</sup>D<sub>0</sub> energy level is hardly affected by the change of Eu<sup>3+</sup> doping concentration. For the GTO:Tb<sup>3+</sup>, with the increase of the Tb<sup>3+</sup> concentration, the fluorescence emission under UV excitation changes from blue-violet region to yellow-green region, which can be ascribed to the influence of CR between Tb<sup>3+</sup> ions. The fluorescence decay behavior reveals that the Tb<sup>3+</sup> ions on <sup>5</sup>D<sub>4</sub> excited state may undergo energy transfer and reabsorption, which can deviate the fluorescence decay from the single exponential model. When the concentration of Tb<sup>3+</sup> is 0.5%, the sample exhibits white light emission with the CIE color coordinates of (0.33, 0.35) and color rendering index of 86. The measurements of temperature-dependent emission spectra show that the above-mentioned phosphors have good luminescent thermal stability. The internal quantum efficiencies (IQEs) of those three types of phosphors are measured, and the IQE of GTO:Eu<sup>3+</sup> is better than those of GTO:Dy<sup>3+</sup> and GTO:Tb<sup>3+</sup>. There is still much room for improvement in the luminescent performance of all these phosphors. These phosphors have potential to be used in UV-excited white LEDs.

Процессы передачи энергии в эвлитите Sr-=SUB=-3-=/SUB=-Y(PO-=SUB=-4-=/SUB=-)-=SUB=-3-=/SUB=-, по отдельности и одновременно легированном ионами Tb-=SUP=-3+-=/SUP=- и Tm-=SUP=-3+-=/SUP=-

In this work the optical spectroscopy and the energy transfer processes involving the Tb3+and Tm3+ ions, have been studied in eulytite double phosphate hosts of the type Sr3Y(PO4)3 doped with various amounts of the two Ln ions. It has been found that several energy transfer and cross-relaxation processes are active in this class of materials, upon excitation in the 5D4 level of Tb, and in the 1G4 one of Tm. In particular, a Tb→Tm transfer of excitation has been found to quench strongly the 5D4 level of Tb. This process occurs with a transfer efficiency increasing from 0.08 to 0.62, for a donor concentration of 2 mol%, and an acceptor concentration increasing from 2 to 15 mol%. The emission spectra are strongly affected by the presence of Tb⟷Tm energy transfer, and Tm→Tm cross relaxation processes.

Manifestation in IR-Luminescence of Cross Relaxation Processes between NV-Centers in Weak Magnetic Fields

Manifestation in IR-Luminescence of Cross Relaxation Processes between NV-Centers in Weak Magnetic Fields

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In this work the optical spectroscopy and the energy transfer processes involving the Tb3+and Tm3+ ions, have been studied in eulytite double phosphate hosts of the type Sr3Y(PO4)3 doped with various amounts of the two Ln ions. It has been found that several energy transfer and cross-relaxation processes are active in this class of materials, upon excitation in the 5D4 level of Tb, and in the 1G4 one of Tm. In particular, a Tb→Tm transfer of excitation has been found to quench strongly the 5D4 level of Tb. This process occurs with a transfer efficiency increasing from 0.08 to 0.62, for a donor concentration of 2 mol%, and an acceptor concentration increasing from 2 to 15 mol%. The emission spectra are strongly affected by the presence of Tb⟷Tm energy transfer, and Tm→Tm cross relaxation processes.

Tailoring Multiphonon Relaxation and Cross Relaxation Energy Transfer in Mixed Ionic-Electronic 20li2o-Xbi2o3-(80-X)Teo2-1er2o3-1ag Glasses at Nir Region

Tailoring Multiphonon Relaxation and Cross Relaxation Energy Transfer in Mixed Ionic-Electronic 20li2o-Xbi2o3-(80-X)Teo2-1er2o3-1ag Glasses at Nir Region

Thermal enhancement of 2H11/2→4I15/2 up-conversion luminescence of BaLu6(Si2O7)2(Si3O10):Er3+/Yb3+ phosphors

A series of BaLu6(Si2O7)2(Si3O10):Er3+/Yb3+ phosphors were manufactured by high temperature solid phase reaction method. The X-ray diffraction (XRD) and vary temperature up-conversion luminescence (UCL) under 980 nm laser excitation were measured to analyze the structure and optical thermal behaviors. When the fixed Er3+ concentration is 0.1, the brightest sample appears at Yb3+ concentration 3.0. By adjusting the doping concentration of Er3+ and Yb3+ respectively, the thermal enhancement UCL times of 2H11/2→4I15/2 transitions of Er3+ attain the maximum point while Er3+/Yb3+ is 0.01/3.0. And the thermal enhancement UCL of 2H11/2→4I15/2 transitions of Er3+ is 4.12 times, and the total green luminescence intensity increases 1.97 times at the range of 303–723 K. Additionally, based on fluorescence intensity ratio (FIR) technique, the maximum absolute sensitivity is 0.00645 K−1. The single doped 1.0Er3+ sample has the thermal enhancement UCL of 2H11/2→4I15/2 transitions of Er3+, however the single doped 4.0Er3+ sample does not have, and this indicates that the cross relaxation between Er3+ is unfavorable to thermal enhancement of 2H11/2→4I15/2. The possible vary temperature UCL mechanism was expound. The results manifest that the BaLu2.99Er0.01Yb3.0(Si2O7)2(Si3O10) phosphor can be a good candidate for optical thermometer at high temperature.

A color-tunable persistent luminescence material LiTaO3:Pr3+ for dynamic anti-counterfeiting

In this work, an original color-tunable persistent luminescence (PersL) phosphor based on Pr3+ doped LiTaO3 (LTO) was realized. The PersL emission can be modulated from pale yellow to deep orange-red merely by changing the concentration of Pr3+, which attributed to the concentration quenching resulted from the cross-relaxation (CR) effect. Thermoluminescence (TL) analysis shows that the continuous shallow traps (0.668–0.8 eV) are suitable for PersL. Moreover, it also exhibits excellent photostimulated luminescence (PSL) performance owing to the presence of stable deep traps of 0.916 eV. A possible PersL mechanism of LTO:Pr3+ is put forward to explain this phenomenon. Finally, inspired by this multicolor PersL feature, a quick response code (QR-code) and an arrow pattern are developed, revealing that LTO:Pr3+ is an ideal material for dynamic anti-counterfeiting. Our work is designed to promote the practical applications of PersL materials in information security areas.

Theoretical analyses and configuration optimizations of a LD-pumped 3.9 µm Ho:BYF laser

In this paper, we introduced the theoretical simulation results of output performances for a LD-pumped 3.9 µm Ho:BYF laser by considering two unique kinetic processes named as energy transfer up-conversion (ETU) and cross relaxation (CR). The influence of the pump energy, pump beam waist radius, pump pulse width, and crystal length on the output characteristics was discussed in detail for the Ho:BYF laser. The thermal simulation was also carried out for the Ho:BYF crystal by using a finite element method (FEM). Then, we constructed a LD-pumped experimental system and successfully realized a LD-pumped 3.9 µm laser. Next, some efforts were undertaken for optimizing the curvature radius of an output coupler (OC), focus position inside Ho:BYF bulks, and crystal length, respectively. The maximum energy of 1.87 mJ had been finally obtained after the optimization. By considering the LD-pumped solid-state laser is still rare in the mid-infrared, our study is thought to be useful for the development of a novel compact and efficient laser in the future.

Tm3+ heavily doped NIR-III bioprobe with 1 µm Stokes shift towards deep-tissue applications

Recently developed rare earth ions doped NIR-NIR bioprobes, with excitation and emission both falling in the NIR region, have attracted wide attention due to their deep-tissue penetration, high signal-to-noise ratio, and high imaging resolution. The current NIR-NIR bioprobes focused mainly on the 1.5 µm emission of Er3+. Here, we developed a novel bioprobe utilizing the 1.8 µm emission of Tm3+ upon 0.8 µm excitation. After an inert shell effectively suppressing the surface quenching effect, the strong cross relaxation 3H4 + 3H6 → 3F4 + 3F4 between heavily doped Tm3+ greatly improves the luminescence intensity at 1.8 µm. As a result, the formed Tm3+ based NIR-III bioprobe exhibits better penetration ability of the state-of-the-art Er3+ based NIR-III bioprobe, and holding an even larger Stokes shift beneficial for the multiplexed bioimaging and labeling applications.

Realization of an Optical Thermometer via Structural Confinement and Energy Transfer.

The influence of temperature on a variety of physiological or chemical processes has generated considerable interest, and recently noninvasive lanthanide-incorporated optical thermometers have been considered as promising candidates for monitoring its changes at different scales. Herein, a novel Bi3+-activated Sr3-xGdxGaO4+xF1-x phosphor with tunable color has been constructed by a cooperative cation-anion substitution strategy with to the replacement of [Sr2+-F-] by [Gd3+-O2-]. When x = 0, the sample Sr3GaO4F/Bi3+ possesses a peak wavelength at 438 nm, and this value will shift to 470 nm if x is equal to 1 (Sr2GdGaO5/Bi3+). In addition, photoluminescence tuning from blue to red has been realized successfully by an efficient Bi3+ → Eu3+ energy migration model in Sr2.6Gd0.4GaO4.4F0.6 samples. The specific Bi3+ → Eu3+ energy transfer has been explained by dipole-dipole interactions derived from a model of the Dexter pathway. Intriguingly, the two dopants (a blue signal from Bi3+ and a red signal from Eu3+) possess different thermal responses to increasing temperature. Accordingly, the intensity ratio values are sensitive to the temperature changes. The energy level cross relaxation causes the quenching effect of Bi3+, and the multi-phonon de-excitation mode leads to the thermal quenching of Eu3+. At room temperature (298 K), the determined maximum relative sensitivity (Sr) is 1.27% K-1. Moreover, the absolute sensitivity (Sa) is 0.067 K-1 since the temperature is elevated to 523 K. The collected results are superior to most of the reported optical thermometry materials.

Enhancement of 1532 nm emission in Ce3+, Er3+ co-doped Ca1.5Y1.5Al3.5Si1.5O12

Near-infrared emission material, C e 3 + , E r 3 + co-doped C a 1.5 Y 1.5 A l 3.5 S i 1.5 O 12 has been synthesized via a high-temperature solid-state reaction method. The luminescence intensity of 1532 nm emission excited with 455 nm increases 4.2 times after the introduction of C e 3 + ions because of C e 3 + → E r 3 + radiation-reabsorption energy transfer and nonradiative energy transfer sensitization as well as the 4 I 11 / 2 ( E r 3 + ) + 2 F 5 / 2 ( C e 3 + ) → 4 I 13 / 2 ( E r 3 + ) + C e 3 + ( 2 F 7 / 2 ) cross relaxation between C e 3 + and E r 3 + ions. The result shows that the developed material is convenient to obtain high-efficiency, near-infrared emission using a commercial blue GaN LED as a pumping source.

Red, Green, Blue and IR emitting zirconium Titanate nano composite co-doped with Er3+/Tm3+/Yb3+ synthesized by combustion synthesis

Activation of upconversion emission in visible region and emission in infrared region in tri-codoped (Er3+, Tm3+ and Yb3+ rare earth ions) zirconium titanate nano composites has been attained by synthesizing through solution combustion method. ZrTi1.4O4, serves as host matrix which offers lowest phonon energy at 870 cm−1. PL emission has been recorded by exciting the samples with wavelength of 980 nm in NIR region. X-Ray diffraction patterns confirm crystallinity of the composites. Morphological studies were performed by Field emission scanning electron microscopy. Primary colors, Blue (475 nm), green (520 nm, 530 nm, 540 nm and 550 nm) and red (650 nm and 670 nm) emissions in visible region along with IR emission peaks centered at 1531 nm, 1574 nm, 1646 nm, 1738 nm and 1793 nm were observed. Dominant red emission appearing in the PL spectra is regarded to be due to Multi phonon relaxation and cross relaxations.

Upconversion Visible Light Emission in Yb/Pr Co-Doped Yttria-Stabilized Zirconia (YSZ) Single Crystals

As a development on previous research on single crystals of Pr3+-doped yttria-stabilized zirconia (YSZ), we report here the preparation and optical properties of Yb/Pr co-doped YSZ single crystals with different Yb2O3 concentrations. Results from X-ray diffraction (XRD) and Raman spectroscopy indicated that all of the crystal samples had a cubic phase structure, and transmission was ≥88% in the 550–780 nm range. Photoluminescence (PL) under excitation with a 980 nm laser showed upconversion emission, and several peaks were observed centered on 448 nm, 508 nm, 525 nm, 542 nm, 617 nm and 656 nm. The effects of excited state absorption (ESA), energy transfer upconversion (ETU), cross relaxation (CR), and cooperative energy transfer (CET) on the upconversion luminescence and energy transition mechanism in YSZ crystals were further studied. The fluorescence lifetime of the 3P0 → 3H5 transition at 542 nm reached 207 μs, which shows that the samples are of potential use for laser and fluorescence output.

Trap Assisted Transition Energy Levels of SrF2:Pr3+-Yb3+ Nanophosphor in TiO2 Photoanode for Luminescence Tuning in Dye-Sensitized Photovoltaic Cells

Luminescent nanophosphors as spectral converters offer immense potential for dye-sensitized photovoltaics (DSPV) to harvest wide range of solar spectrum. Herein, we demonstrate a novel structural design of DSPV by employing downconverting ( dc ) nanophosphor layer in TiO2 photoanode for indoor (ambient) applications. Cubic SrF2:Pr3+-Yb3+ nanoparticles are synthesized by template-free hydrothermal technique. The dc nanophosphor absorbs photons of blue region leading to emission of broad luminescence band (green and red), which is well-matched with N719-dye absorption. For the first time, we have designed a unique Pr3+-Yb3+ co-doped dc system yielding tuned and intensified luminescence by effective cross-relaxation (CR) with back energy transfer (BET) mechanism and demonstrated efficient working of the dc nanophosphor layered DSPVs under indoor LED light (Warm-3200K; Day-5000K) conditions. The dc-DSPV achieved high PCE of 14.85 and 15.9% respectively under indoor low light conditions (1000 lux). This approach resulted in 63.44% increment in output power density for dc-DSPV compared with control-DSPV under LED-3200K irradiation. These findings suggested that this configuration of dc -layered DSPV can provide new strategy for future indoor electronic-operations under ambient light conditions. Keywords: DSPV, downconversion, SrF2:Pr3+-Yb3+, luminescence tuning, trap assisted transition energy levels, interfacial charge transport kinetics and indoor light condition. Acknowledgement: This work was supported by Brain Pool Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT, Korea. (Grant number: 2019H1D3A1A01071183). It was also supported by the Technology Development Program to Solve Climate Changes of the National Research Foundation, funded by the Ministry of Science, ICT & Future Planning (No: NRF-2016M1A2A2940912). Figure 1

Photoluminescence and energy transfer studies in Ce3+-Sm3+ co-doped phosphate glasses

0.5Ce3+-xSm3+ (x = 0.11, 0.68 and 1.05 mol%) co-doped phosphate glasses were successfully synthesized via melt-quenching method and analyzed using absorption, photoluminescence and decay curves. According to Judd-Ofelt formalism, the Ω2, Ω4 and Ω6 parameters were determined and used to obtain some radiative properties. With the increasing of Sm3+ concentration, it was noticed the decrease of emission peak intensity and decay curves of Ce3+ due to the energy transfer Ce3+→ Sm3+. Moreover, it was observed that the intensity of Sm3+ emission increases until 0.68 mol%, then decreases for the 1.05 mol% Sm3+ concentration. According to the decay curves of Sm3+, this decreasing can be explained by the cross relaxation between Sm3+ ions. The calculated lifetimes by Judd-Ofelt theory and the experimental lifetimes for the prepared phosphate glasses were obtained. The dependence of the emission intensity on the concentration of doping ions has been explained using energy transfer models in order to obtain the optimum Sm3+ concentration.